1. Field of the invention
The present invention relates to a read-out device for use in performing a radiation image recording and reproducing method employing a radiation image storage panel having a stimulable phosphor.
2. Description of prior art
As a method for obtaining a radiation image, there has been conventionally employed a radiography utilizing a combination of a radiographic film having a sensitive silver salt material layer and an intensifying screen. As a method replacing the above-mentioned conventional radiography, a radiation image recording and reproducing method employing a stimulable phosphor as described, for instance, in Japanese Patent Provisional Publication No. 55(1980)-12145, has been developed and paid much attention. In this method, a radiation image storage panel (a stimulable phosphor sheet) having a stimulable phosphor is used and this method involves steps of causing the stimulable phosphor in the panel to absorb a radiation having passed through an object or having radiated from an object; exciting (or scanning) the phosphor with an electromagnetic wave such as visible light or infrared rays (i.e., stimulating rays) in time sequence to release radiation energy stored in the phosphor as light emission (i.e., stimulated emission); photoelectrically reading out the emitted light to obtain electric signals; and visualizing the electric signals as an image.
The radiation image storage panel used in the radiation image recording and reproducing method is sometimes called a stimulable phosphor sheet. Generally, the stimulable phosphor sheet comprises a support and a phosphor layer provided on one side thereof and is in the form of a sheet of rectangle, square, etc. (one side having a length of about 20 to 50 cm). Generally, a transparent protective film made of a plastic film is provided on the surface of the phosphor layer to protect the phosphor layer from chemical denaturation or physical shock.
The phosphor layer comprises a stimulable phosphor and a binder for retaining the phosphor in a dispersed form. The stimulable phosphor has such a property that when it is irradiated with a radiation such as X-rays, it is caused to absorb the radiation and then it emits light (stimulated emission) when excited with an electromagnetic wave such as visible light or infrared rays (i.e., stimulating rays). Thus, a radiation having passed through an object or having radiated from an object is absorbed by the phosphor layer of the panel in proportion to the amount of the radiation and a radiation image (radiation image information) of the object is formed as a radiation energy-stored image on the panel. When the panel is excited with an electromagnetic wave in time sequence, the radiation energy-stored image is released as stimulated emission. The stimulated emission is photoelectrically detected to obtain electric signals to reproduce the radiation energy-stored image of the object as a visible image.
In the radiation image recording and reproducing method, a radiation image is obtainable with a sufficient amount of information by applying a radiation to the object at a relatively small dose as compared with the conventional radiography. Accordingly, the radiation image recording and reproducing method is of great value, especially when the method is used for medical diagnosis by a radiography with X-rays.
Further, it has been found that the method can be advantageously used for the case where autoradiography is carried out in isolating and identifying high-molecular weight materials such as protein, nucleic acid, etc. originating from organisms and evaluating their characteristics.
In carrying out the radiation image recording and reproducing method employing the radiation image storage panel, there is conventionally used a system wherein a recording means for recording a radiation image on the panel, a read-out means for photoelectrically reading out the radiation image and an erasure means for erasing the remaining radiation image on the panel after read-out operation are separately provided or a device wherein the recording means, the read-out means and the erasure means are provided in a combination. Particularly, when the radiation image recording and reproducing method is performed by using a system wherein the recording means and the read-out means are separately provided, each panel is placed in a cassette (a light-shielding case) to prevent information on an image recorded and stored in the panel from being lost by exposure and lowering in the quality of a reproduced image from being caused thereby. The recording of the radiation image is made on the panel as placed in the cassette and the cassette is then fixed to the read-out means where the panel is taken out of the cassette and the read-out operation for the radiation image stored in the panel is conducted. Generally, the removal of the panel from the cassette is done by a cassette-removing means comprising a sucker provided within the system.
When the panel having the radiation image recorded and stored therein is exposed by allowing it to stand in a light room, the degree of loss of the radiation image is relatively low, when the exposure time is very short. However, when the panel is used for medical diagnosis, radiation image information is information on the human body (X-ray photograph of a region of the human body) and hence the image must be obtained with high accuracy.
In the radiation image information obtained by utilizing autoradiography, the image information is to be locational information (image information being recognized by a pattern) on the electrophoretically resolved pattern of radioactively labeled nucleic acid-cleavage products. Thus, not so much high resolution and accuracy are required for the image, as compared with the case for medical use. Therefore, it is not always necessary that the panel as placed in the cassette is fixed to the read-out means. It may be contemplated that the panel which is not placed in the cassette is fixed to the read-out means. In the case where the panel is not placed in any cassette, the means for taking the panel out of the cassette can be omitted, the system can be made compact and the manufacturing cost of the read-out means can be reduced.